As conventional techniques for preparing an ultra fine fiber or nano fiber suitable for the production of an artificial leather, there are known a sea-island type conjugated spinning method, a split type conjugated spinning method, a blend spinning method and the like However, in case of the sea-island type conjugated spinning method or the blend spinning method, one of two polymer components consisting of a fiber must be dissolved and removed to make the ultra fine fiber. In order to produce artificial leather from fiber prepared by these methods, a complex process must be carried out, including melt spinning, fiber production, non-woven fabric production, urethane impregnation and single component dissolution.
Nevertheless, it is impossible to produce a fiber with a diameter of less than 1,000 nm by the above two methods.
In case of the spit type conjugate spinning method, it is problematic in that since two polymer components (for example, a polyester and a polyamide) with different dyeing properties co-exist in the fiber, uneven dyeing is exhibited and the artificial leather production process is complicated. In addition, it is difficult to produce a fiber with a diameter less than 2,000 nm by the above method.
Another conventional technique for preparing nano fibers is the electrospinning method. In the electrospinning method, as shown in FIG. 4, a polymer spinning dope in a spinning dope main tank (20) is continuously and constantly fed to a plurality of nozzles (2), to which a high voltage is applied, through a metering pump (21). Subsequently, the spinning dope fed to the nozzles (2) is spun and collected through the nozzles (2) on a collector (4) of an endless belt type having a high voltage of more than 5 kV, thereby producing a fiber web. The fiber web produced is needle-punched in the next process to produce a non-woven fabric composed of nano fibers.
As seen from above, the conventional electrospinning method can produce only a web or non-woven fabric composed of a nano fiber less than 1,000 nm. Hence, to prepare a continuous filament by the conventional electrospinning method, the produced nano fiber web has to be cut to a predetermined length to produce a staple and this staple has to undergo an additional spinning process to produce spun yarn, which makes the process complicated.
In case of the non-woven fabric composed of nano fiber, there is a limitation to employing the non-woven fabric to various fields of application, such as the artificial leather, due to the limits in the physical properties of the non-woven fabric. For reference, it is difficult to achieve physical properties of more than 10 MPa from non-woven fabric composed of nano fiber.
The present invention is intended to prepare a continuous filament composed of nano fiber utilizing a simple procedure of providing a process of continuously preparing a filament (yarn) using electrically spun nano fiber web, without any additional spinning process. Additionally, the present invention is intended to provide a continuous filament of nano fiber which is superior in physical properties and is suitable for various industrial materials, such as filters, diapers, sanitary pads, artificial vessels and so on, as well as artificial leather.